The present invention relates to an airbag development control apparatus which develops an airbag by detecting a collision of a vehicle.
Such an airbag development control apparatus shown in FIG. 5 has been generally known.
The conventional airbag development control apparatus shown in FIG. 5 includes an acceleration sensor (G-sensor) 2, an electronic control unit 11 and inflators 9 and 10. An airbag which is not shown is configured to be developed by the above-mentioned two inflators 9 and 10.
In the conventional airbag development control apparatus, when a vehicle collides, acceleration at the time of collision is detected by the acceleration sensor 2, and detection signals of the acceleration outputted from the acceleration sensor 2 are subjected to arithmetic processing such as integration by the electronic control unit 11 to calculate a collision speed. When the collision speed is less than a first threshold value, neither the inflator 9 nor the inflator 10 is operated. When the collision speed is more than the first threshold value but less than a second threshold value, only the inflator 9 is operated to partially develop the not-shown airbag, whereas when the collision speed is more than the first threshold value and the second threshold value, the inflator 10 is operated after the inflator 9 is operated to fully develop the not-shown airbag.
In addition, another airbag development control apparatus shown in FIG. 6 has also been known.
The airbag development control apparatus shown in FIG. 6 includes an initial collision detecting unit 1a disposed at an anterior end of a vehicle, a collision determining unit 1b disposed in the center of the vehicle (in the vicinity of a shift gear), AND gates 12, 13 and inflators 9, 10. Each of the initial collision detecting unit 1a and the collision determining unit 1b is embedded with an acceleration sensor.
In the conventional airbag development control apparatus of FIG. 6, the initial collision detecting unit 1a detects acceleration signals generated in the initial stage of collision to output first collision determination signals X1 and also detects acceleration signals generated in the stage posterior to the initial stage of the collision to output second collision determination signals X2. The collision determining unit 1b detects acceleration signals of a level in the initial stage of the collision to output third collision determination signals Y1, and also detects acceleration signals generated in the stage posterior to the initial stage to output fourth collision determination signals Y2. Wherein, the inflator 9 is operated to partially develop a not-shown airbag by utilizing signals which are based on an AND operation of the first collision determination signals X1 and the third collision determination signals Y1, and the inflator 10 is operated to fully develop the not-shown airbag by utilizing signals based on an AND operation of the second collision determination signals X2 and the fourth collision determination signals Y2.
Here, it is to be noted that each of the above-described first to fourth collision determination signals X1, X2, Y1 and Y2 are generated based on signals in which the acceleration signals are processed with integration processing.
In development control of the airbag, judgment on the development of the airbag is performed by algorism such that an event of collision is detected and the airbag is developed at the most appropriate timing. Each of the conventional airbag development control apparatuses described above performs the integration arithmetic of the signals detected by the acceleration sensor and utilizes a result of the integration arithmetic as the judgment on the development of the airbag, in accordance with collision detecting algorism.
However, in the judgment on the development of the airbag utilizing the algorism, an integration value does not make a significant difference in a value immediately after the collision depending upon a structure of vehicle or a mode of collision, so that it is difficult to appropriately differentiate and satisfy following requirements which are to be stipulated in the North American regulation in the future.
1. Performing depowered development of the airbag when the vehicle collides head-on at 26 kph.
2. Performing full development of the airbag at 64 kph according to ODB (Offset Deformable Barrier) collision.
3. Performing full development of the airbag when the vehicle collides at an angle at 48 kph.
In addition, it is necessary to make decision on the judgment of the development approximately 30 milliseconds (0.03 second) before the acceleration which causes damage to an occupant is generated, in anticipation of the time required for the airbag to expand. However, the judgment of the development is delayed when intensity of the collision is judged at the time when the difference in the integration value is occurred.
FIG. 7 shows curves each representing an integration value of acceleration signals detected by an acceleration sensor disposed in the center of a vehicle. Wherein, a curve A represents a case when the vehicle is collided head-on at 26 kph, a curve B represents a case when the vehicle is collided at 64 kph according to the ODB collision, and a curve C represents a case when the vehicle is collided at an angle at 48 kph.
As is apparent from FIG. 7, there is virtually no difference in the integration values represented by the curves A to C in the vicinity of 30 milliseconds after occurrence of the collision (inside of a circle indicated by “D” in the drawing). Hence, differentiation of the mode of collision is difficult.
Also, the above-described conventional airbag development control apparatus shown in FIG. 6 provides the acceleration sensor in each of the initial collision detecting unit 1a disposed at the anterior end of the vehicle and the collision determining unit 1b disposed in the center of the vehicle to carry out the development control of the airbag by utilizing the mutually different acceleration signals which are generated by the two acceleration sensors. Accordingly, there is also a problem in the conventional airbag development control apparatus that a circuit for signal processing becomes complicated, resulting in increased cost.